Photographic products



United States Patent 3,155,516 PHOTOGRAPHIC PRODUCTS Ralph Kingsley Blake, Westfield, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Nov. 8, 1962, Ser. No. 236,418 9 Claims. (Cl. 96-107) The invention relates to photography, and more particularly to new photographic products useful therein.

The principal processes of photography are based on the use of colloid-silver halide emulsion layers. In the prior art processes a latent image is formed by imagewise exposure of a radiation-sensitive silver halide emulsion layer. Silver halide bearing a latent image has been developed to silver by selective reduction in these instances.

In the prior processes of photography the unreduced silver remaining after development has been removed by silver halide solvents or rendered insensitive or transparent by treatment with complexing agents. Optional after-treatments include intensification and reduction, toning and tinting. However, the primary or first step in image formation always has been based on the selective reduction step.

It is an object of this invention to provide new photographic silver halide compositions, photographic layers and photographic elements bearing a layer of silver halide. Another object is to provide processes for making these products. A further object is to provide such prod ucts which are adapted to more versatile processes for forming silver and other images and which are simple, dependable and give results equal in quality to the prior conventional methods. Still further objects will be apparent from the following description of the invention.

The objects of this invention are realized by new silver halide compositions and layers in which images are formed, after exposure to actinic radiation, by imagewise solution of the silver halide. The residual silver halide image may then be converted to silver, dyed or toned images.

The novel photographic compositions and silver halide layers of this invention comprise silver halide crystals which have been treated, in substantially greater than fog-inhibiting amounts, with an organic mercaptan containing 1-2 mercapto groups taken from the group consisting of alkyl mercaptans and organic mercaptans containing two mercaptan groups linked to carbon and having a molecular weight greater than 75. These compounds can be represented by the respective formulae:

where R is an alkyl radical of 3-20 carbons, preferably 3l2 carbons, and where R is a divalent organic radical. The latter can be hydrocarbon radicals or such radicals substituted by alkyl, alkoxy, carboxylic, halogen and cyano groups. The silver salts of these compounds are less soluble in water than untreated silver chloride. Tautomeric forms of the organic compound may result in different linkages for the hydrogen atom than shown in the formula, e.g.,

HR=S or HSR(H)=S The compound, RSH or HSRSH, is characterized in that when admixed with an aqueous silver halide dispersion it protects the silver halide crystals to such an extent that when a silver halide dispersion protected by said compound is treated with 10%, by weight,

" 3,155,516 Ce Patented Nov. 3, 1964 aqueous sodium thiosulfate, at least three times the amount of silver halide remains undissolved as in a similar dispersion successively treated with 5% aqueous sodium hypochlorite and 10% aqueous sodium thiosulfate, after vigorous agitation of the dispersions for 30 seconds at 25 C. The dispersion so successively treated clears, Whereas the other dispersion remains turbid.

Preferably, the silver halide crystals are dispersed in a water-permeable organic colloid to form a light-sensitive photographic emulsion. The selected aliphatic mercapto or dimercapto compound can be added to the silver halide emulsion while the latter is in the liquid state or the emulsion may be coated on a suitable support and the resulting element bathed or impregnated with a solution, e.g., an alcoholic solution of the organic compound. In the working examples below, the amount of organic compound in the silver halide emulsion is from about 0.125 to 314 g. per mole of silver halide but wider ranges of concentration can be useful, depending upon the particular organic compound, the size and nature of the silver halide crystals, the presence of other materials which may partially cover the surface of the silver halide crystal, and upon various other factors.

The gelatin:silver halide ratio is quite flexible and may vary from 3:1 to 1:30 depending on the particular organic compound and application.

In one commercially practical aspect of the invention, the silver halide is present in much higher concentra' tion than in conventional emulsions and emulsion layers.

In an important use of the novel products of the invention, direct positive images can be formed by a process which comprises (a) Exposing imagewise to actinic light a photo-sensitive layer comprising silver halide crystals treated with the organic compound as described above,

(b) Treating the exposed layer in a solution of a silver halide solvent to remove soluble silver halide in the exposed image areas, thus forming a positive silver halide image, and

(0) Washing the resulting layers.

If desired, the silver halide image may be viewed directly, e.g., by projection (if on a transparent support) or it may be intensified by (d) Converting the residual silver halide to silver by treatment in a fogging developer, e.g., a high pH, l-phen yl-4-methyl-3-pyrazolidone/hydroquinone developer containing iodide ion or by fogging the emulsion by exposure to light and then treating with a silver halide reducing agent, e.g., a conventional silver halide developer, and

(e) Washing the developed layer to reveal a positive silver image in the original non-exposed areas.

The imagewise solution of the exposed silver halide/organic compound stratum may be effected by the silver halide solvent commonly used as photographic fixing agents, e.g., sodium thiosulfate, sodium thiocyanate, concentrated solutions of potassium bromide, etc. Reduction of the treated, residual silver halide may be accomplished by use of any chemical reducing agent capable of reducing silver ion to silver metal, e.g., hydroquinone, metol, sodium hydrosulfite and stannous chloride. The function of the reducing agent may be enhanced by modifying the surface properties of the treated, residual silver halide crystals by means of alcohol, thiourea, potassium iodide, etc The silver halide image may be toned, e.g., with sodium sulfide, sodium selenide, etc. In addition, color images may be obtained by developing the treated, residual silver halide with a primary aromatic amine color developing agent in the presence of a color coupling compound either in the developing bath or previously incorporated in the emulsion.

Since a broad new photographic principle has been discovered, the applicant does not wish to be limited to a narrow class of aliphatic mercapto or dimcrcapto compounds with which the silver halide crystals may be treated in preparing the novel compositions of this invention. Instead, a number of useful compounds will be shown in the exemplary disclosure and a straightforward and relatively simple test will be described by which one skilled in the art may readily determine whether or not other given organic compounds will have utility in this invention. Essentially, the test consists of two parts, Test A and Test B. In Test A, the candidate aliphatic mercapto or dimercapto compound must render a dispersion of silver halide crystals insoluble in a silver halide solvent, i.e., an aqueous solution of sodium thiosulfate, at some pH between 1 and 13. If the candidate compound effects the insolubility required of Test A, it must also, to have utility, pass Test B by forming with said dispersion of silver halide crystals a reaction product which, upon treat ment with an aqueous solution of sodium hypochlorite, becomes soluble when subsequently treated with aqueous sodium thiosulfate. The following practical tests are provided in further exemplification of the invention and include specific concentrations of solutions, times, etc., so that suitable organic compounds may be readily and positively identified.

TEST A A solution nearly saturated at 25 C. with a candidate organic compound is prepared using ethanol, acetone, dimethyl formamide, water or other suitable solvents. Depending on the solubility, a solution concentration from 0.01 to percent by weight is obtained. Twenty-five ml. of a silver chlorobrornide dispersion containing mg. of silver halide (calculated as silver bromide), prepared as described below, is treated with small increments (i.e., about 0.1 to 0.2 ml. at a time) of the said candidate solution under safelight conditions (Wratten 1A red filter or equivalent) until the silver halide dispersion either is rendered insoluble in 10% aqueous sodium thiosulfate or the candidate is found not to cause insolubilization. Generally insolubilization will occur upon the addition of 0.05 g. or less of said candidate compound, calculated as the pure compound. Compounds which must be used in substantially greater quantities than this, e.g., 12 g. to etfect insolubilization are considered less preferred compounds. bility is determined by taking a 0.5 ml. portion of the silver halide dispersion (after each incremental addition of the candidate organic compound), adding about 0.1 to 0.2 ml. of 10% aqueous sodium thiosulfate solution and observing the turbidity after seconds.

As a control, one should use 25 ml. of water to which small increments of the candidate solution are added. Halfanilliliter portions of the control are treated in the same manner with the sodium thiosulfate solution. The presence of visual turbidity relative to the control is sufficient to satisfy the definition of insolubility in this test.

This test may be repeated for various pH increments from 1 to 13. Although there is some optimum pH value at which the test is most sensitive, this is not a sharp maximum which must be precisely attained. Rather, it has been found that there is a fairly broad range of pH values (e.g., 2.0 to 3.0 pH units) over which the test has a satisfactory sensitivity. In practice, the silver halide dispersion might be tested without adjustment (e.g., at pH 5.0 to 7.0) and if insolubilization occurs here, Test A is completed. If there is no insolubilization, the test is repeated at a higher pH (e.g., about 11-13). If there is still no insolubilization, the test is conducted with emulsion adjusted to a lower pH (e.g., about pH 1-3). Thus three dilferent pH values represents a practical maximum num- The silver halide dispersion insoluher which must be investigated to determine whether or not insolubilization will occur.

TEST B An organic compound capable of insolubilizing a silver halide dispersion according to Test A is now ready for the next test, which again will be conducted under safelight conditions. To the above silver halide dispersion, there is added the minimum amount of a solution of the candidate organic compound found necessary for insolubilization. Half milliliter samples of the dispersion containing 0.5 mg. of AgBr or 0.29 mg. Ag are placed in two test tubes. To one sample is added 0.5 ml. of water; to the other is added 0.5 ml. of a 5% by weight aqueous solution of sodium hypochlorite (containing 25 mg. sodium hypochlorite. Next, there is added to both samples, 1.0 ml. of an aqueous 10% by weight solution of sodium thiosulfate (containing mg. sodium thiosulfate). If, after standing for up to thirty seconds, the sample treated with sodium hypochlorite clarifies (or becomes less turbid) relative to the control sample, the candidate organic compound meets the requirements of Test B and and it is satisfactory for use as disclosed in this invention.

Silver Halide Dispersion Preparati0lzDispersiolz I The silver halide dispersion disclosed in Tests A and B is prepared according to the following specifications. In red light, 30 g. of photographic grade gelatin is soaked in 1100 ml. of distilled water for 10 minutes. The temperature is then raised to 120 F. and g. of solid ammonium chloride added. The mixture is stirred at F. and after the ammonium chloride is completely dissolved, a solution made by diluting 500 ml. of 3 N silver nitrate with 2000 ml. of distilled water is added while stirring the solution for 5 seconds. This mixture is held at 120 F. for 4 minutes with stirring, and then ml. of 3 N ammonium bromide added (30 mole percent) in 10 seconds. The mixture is held an additional 15 minutes at 120 F. with stirring and then cooled to 100 F. A mixture of 75 g. of the sodium salt of technical lauryl alcohol sulfate (a White powder) and 7 ml. of 3 N sulfuric acid is added in 10 seconds to the silver chlorobromide, stirring continued for one minute and then the mixture allowed to settle. The supernatant liquid is decanted and replaced by 2000 ml. of distilled water containing 4 g. of sodium chloride. This mixture is stirred for 5 minutes at 100 F., allowed to settle and decanted again. Two hundred ml. of distilled water is added to the silver halide curds and the temperature adjusted to 95 F. This mixture is vigorously stirred for 10 minutes at 95 F. and then the pH adjusted to 6.1i0.1 with aqueous sodium hydroxide solution. The redispersed emulsion is then analyzed for silver halide content calculated as silver bromide and a dispersion made by diluting the appropriate amount with distilled water such that the dispersion contains 1 mg. calculated silver bromide per ml.

Particularly preferred organic compounds of the formulae wherein R is a monovalent aliphatic radical and R is a divalent organic radical, are those which form silver salts of the formulae Among the useful silver salts of the above formula are those which are said salts being insoluble in aqueous ammonium hydroxide at pH 12.

Dispersed crystals of silver halide, treated with a suitable organic compound of one of the above formulae, are affected by exposure of a portion of said crystals to actinic radiation, e.g., ultraviolet, visible, infrared, X- radiation, etc., to such an extent that at least 20% of the less soluble crystals remain after 90% of the more soluble crystals dissolve when treated in by weight aqueous sodium thiosulfate solution. Generally, the presence of solubilizing groups in the R or R' portion of the above formulae should be avoided in order that reaction products with silver halide will be formed which will significantly reduce the solubility of silver halide grains in silver halide solvents. There are exceptions to this rule, particularly in the case of suitable compounds containing solubilizing groups which are compensated for by the presence of insolubilizing groups, e.g., long chain alkyl groups. The chemical testing for selecting suitable compounds has been found to give absolute correlation, i.e., organic compounds which have been subjected to the pair of tests have produced Without exception when tested in actual photographic emulsions, the very effects predicted by said tests. Combinations of the compounds with various basic dyes, including various cyanine dyes, and Methylene Blue (Colour Index No. 922) Crystal Violet AO (Colour Index No. 681) and Rhodamine 6 GDN Extra (Colour Index No. 752) have proven useful additions.

The silver halide need not be a combination of silver chloride and silver bromide, but may be silver chloride, silver bromide and other mixed halide systems conventional in photographic practice, e.g., silver bromoiodide. While, for rapid processing, a high silver halide to binder ratio is preferred, more conventional ratios can also be used.

In place of part of the gelatin, other natural or synthetic water-permeable organic colloid binding agents can be used and in some cases such binders can be used alone. Such agents include water-permeable or water-soluble polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, ethers and acetals containing a large number of intralinear CH -CHOH groups, hydrolyzed interpolymers of vinyl acetate and unsaturated addition polymerizable compounds such as maleic anhydride, acrylic and methacrylic acid esters and styrene. Suitable such colloids of the last-mentioned type are dis closed in US. Patents 2,276,322; 2,276,323 and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde acetal, poylvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents which can be used include the poly-N- vinyllactains of Bolton US. Patent 2,495,918, various polysaccharides, e.g., dextran, dextrin, etc., the hydrophilic copolymers in Shacklett US. Patent 2,833,650, hydrophilic cellulose ethers and esters, and polymers of acrylic and methacrylic esters and amides. Also, it has been found practical to treat silver halide layers on a base material in the essential absence of a binder, e.g., by chemical or vacuum deposition.

The emulsions may optionally contain any of the usual adjuvants customarily employed in silver halide systems so long as they do not interfere with the adsorption and complexing action of the essential ingredient of the invention.

The emulsions can be coated on any suitable support, e.g., cellulose esters, cellulose mixed esters; superpolymers, e.g., polyvinyl chloride (co) vinyl acetate, polyvlnyl acetals, butyrals; polystyrene; polyarnides, e.g., polyhexamethylene adipamide, polyesters, e.g., polycarbonates, polyethylene terephthalate, polyethylene terephthalate/ isophthalate, esters formed by condensing terephthalic acid and its derivatives, e.g., dimethyl terephthalate with' propylene glycol, diethylene glycol, tetramethylene glycol, cyclohexane-1,4-dimethanol (hexahydro-p-xylene dialcohol); paper, metal, glass, etc.

As disclosed earlier, the desirable concentration of the selected organic compound depends on many factors such as the size and solubility of the organic compound, the nature of its reaction with silver halide, the size and nature of the silver halide crystals, the presence of other materials which may react with or be adsorbed to the surface of the silver halide, etc. In Example III below, a number of organic compounds are disclosed which were tested in a dispersion of silver halide crystals wherein the average grain size was 035 (micron) in diameter, therefore about O.043 in volume, assuming cubic grains. The silver halide comprised 70 mole percent silver chloride and 30 mole percent silver bromide, with a specific density of about 5.7 g./cc. or 5.7 10 g./,u The weight per individual crystal or grain is 0.043/L3X5.7 10 12 g./ .t =0.25 10 g. Assuming a molecular weight of 157 for the mixed AgCl-AgBr crystals, and dividing this number by the weight per grain, gives 157 g./mole+0.25 1t) g.=6.3 10 grains/mole. The area of a cubic grain of 0.35;; diameter=6 .25 =.74,u, which, multiplied by the 6.3 x10 grains per mole, gives a molar surface area of 4.6 1O u or 4.6 l0 square angstroms.

A particularly preferred aliphatic mercaptan is n-dodecyl mercaptan (or dodecanethiol). Assuming that a single molecule of the compound could occupy an area of thirty square angstroms, it would require 1.5 1O molecules to occupy a molar surface area of silver halide. With a molecular Weight of 202, this would require of n-dodecyl mercaptan to insolubilize one mole of the silver halide. As disclosed in Example IV in a photographic emulsion coated on a film base support it was found that 0.4 g. of n-dodecyl mercaptan per mole of silver halide gave optimum results. Thus the experimental values are in good agreement with the theoretically determined amount of n-dodecyl mercaptan required to cover the silver halide surface.

It has also been found that elements suitable for this novel process can be prepared by bathing a photographic film in a solution of an appropriate organic compound. In this embodiment, the silver halide crystals near the surface of the coated emulsion stratum are in contact with a higher concentration of the organic compound. Crystals farther from the surface, are treated with less of the organic compound and, if the rate of diffusion is sufiiciently slow, there may be considerably less of the organic compound (even approaching zero) reacting with the lower than with the surface silver halide crystals. In such elements, satisfactory results might be obtained with only a fraction, e.g., one-half, of the amount of the organic compound theoretically calculated as required to just cover the surface of a mole of the crystals.

The invention will be further illustrated by but is not intended to be limited to the following examples:

EXAMPLE I A photographic element was prepared by coating an aqueous gelatin dispersion of silver chlorobromide (70 mole percent silver chloride and 30 mole percent silver bromide) on a film base prepared as described in Example IV of Alles US. Patent 2,779,684. The dispersion had a ratio of silver halide to gelatin of 28:1 by weight and was coated at a pH of 6 at a rate of 116 milligrams of silver halide per square decimeter. After drying, the element was bathed for about 15 seconds in a dilute aqueous solution of n-dodecyl mercaptan having a pH of 5.1 and dried. The solution of n-dodecyl mercaptan was prepared by diluting 5 m1. of a stock solution (1 gram of the compound made up to ml. in ethanol) with an additional 20 ml. of ethanol and 10 ml. of Water. The dried element was then exposed behind a photographic transparency for 15 seconds to the radiation from a General Electric 2A photoflood lamp at a distance of about 6l0 inches. The exposed element was then immersed in a 12.8% aqueous solution of sodium thiosulfate for 30 seconds resulting in removal of the silver salt in the exposed areas. Subsequently, the fixed film was then rinsed briefly in water and bathed in a rapid acting fogging developer solution comprising l-phenyl- 4-methyl-3-pyrazolidone and hydroquinone as reducing agents to which there had been added potassium iodide and a direct positive image formed. All of the above operations were carried out in ordinary fluorescent room illumination.

Where a more sensitive product is prepared by appropriate selection of such factors as grain size, silver halide composition, etc., it may be desirable to use conventional photographic darkroom handling of the element prior to the image exposure. During the developing step, the treated element is converted into an exact reproduction (i.e., direct positive image) of the original transparency. After brief washing in water and drying, it is satisfactory for use in any application where an exact reproduction is desired, e.g., in the graphic arts field, for a projection transparency, etc.

EXAMPLE II Example I was repeated except that ethylcyclohexyl dimercaptan was substituted for the n-dodecyl mercaptan of that example and the exposed element was immersed in the 12.8% aqueous solution of sodium thiosulfate for only 10 seconds instead of 30 seconds. As in Example I, a direct positive image was obtained.

In connection with the above examples, it has been found that the pH of the treating solution used to initially bathe the film has a striking effect. With very low pH the effect of the treatment is minimized or completely eliminated. It should be appreciated from the above that while all of the compounds produce desirable results over a wide pH range, each compound apparently has an optimum pH range which is most effective. It will be apparent to one skilled in the art that simple tests can be run to establish the best pH conditions for operation.

EXAMPLE III Tests A and B have been described earlier as procedures whereby one can determine Whether or not a given dimercaptan or aliphatic mercaptan is suitable for use according to the process of this invention. Some of the compounds which were indicated as suitable according to the screening procedures of both tests, have been incorporated into actual photographic coatings and good results have been obtained. Below there are listed a number of the mercaptans of this invention which were tested in this manner including a few of the compounds which have been found to be inoperable. Among the compounds found unsuitable, most failed to produce the insolubility required of Test A and were therefore not subjected to further testing. Since it was impracticable to perform complete photographic experiments with each and every compound screened according to Tests A and B, a simulated photographic test was devised and will be designated as Test C. It is noted that there is complete testing correlation in that any compound which was found suitable according to the photographic test to be described in the next paragraph was also found suitable according to Tests A and B.

TEST C A 0.5 ml. portion of the insolubilized dispersion prepared in Test A under safelight conditions is placed in a 12 x 75 mm. Pyrex test tube three inches from a No. 2 reflcctoflood lamp. This insolubilized dispersion is exposed to the lamp for up to 10 minutes. A control consisting of another 0.5 ml. portion of the insolubilized silver halide dispersion from Test A is taken under safelight conditions. Two-tenths of a milliliter of 10% aqueous sodium thiosulfate is added to each of the dispersion samples taken and compared under safelight conditions. Any reduction in turbidity of the dispersion exposed to the refiectofiood lamp compared to the unexposed control after treatment with aqueous sodium thiosulfate solution shows that photosolubilization occurs.

Tests A, B and C were all conducted using Silver Halide Dispersion I, the preparation of which was given immediately following the description of the procedure for Test B. To determine in approximate minimum concentration of the organic compound required to effect insolubilization of silver halide in the presence of an aqueous solution of sodium thiosulfate, the qualitative procedure of Test A was repeated in a more quantitative manner, using a ripened, washed and redispersed (but not chemically sensitized) gelatino-silver chlorobromide emulsion as described in Example I of assignees copending application, Nottorf, U.S. Serial No. 94,989, filed March 13, 1961. This emulsion is designated in the table below as Dispersion II, and was made as follows: A lithographic emulsion having a silver halide composition of 30 mole percent AgBr and 70 mole percent AgCl and having 20 grams of gelatin present per mole of silver halide for the steps of precipitation and ripening was freed of unwanted, soluble, by-product salts by a coagulation and wash procedure as taught in Waller ct al. US. Patent 2,489,341, wherein the silver halide and most of the gelatin were coagulated by an anionic wetting agent, sodium lauryl sulfate, using an acid coagulation environment. Following the washing step, the emulsion coagulate was redispersed in water together with 47 grams of additional bulking gelatin.

DIMERCAPIANS Test Results with Dispersion I Gms. Compound to Insolubilire Compound Dispersion II Insolublll- Chemical Photosolu- Containing 25 mg zation Test Solubilization bilization Silver Halide A Test B Test; 0

1. 2,3-quinoxalinedithiol Insoluble- Soluble 0, 001 2. 2,3-dirnereaptopro anol- 0.0008 3. loluene-3,4-dithio 0. 0001 4. Glycol dlmercapto acetate 0. 0M 5. Cyclohexane-1,1-dithio1 0.001 6. 2,5-dimercapto-l,2,3,4-thiadiazole 0.0001 7. 5,5-thiobis-(1,3,44zhiadiazole-2-thiol) 0. 0002 8. 3,5-dimereapto4-cyano-1,Hhiazole.--- 0.0010 9. Ncyano imine dipotassium dithiolate 0. 04 10. 1,1-d1eyano2,2-disodium dithlolate ethylene 0. 02 11. 2-cyano-3,3-disodiurn dithiolate aerylamide 0.02 12. 2-cyano-3,3-dipotassium dithiolate ethyl acrylatc 0. 0?. l3. Ois-dicyanoethylene disodium thiolate- 0.01 14. Trnns-dicyano dithiolate ethylene ditet methylammonium salt 0. 01 15. 3,.idisodium dithlolate-et-cyano-1,2-thiaz0le*. 0. 05

See footnote at end of table.

ALIPHATIC MERCAPTANS OR SULFIDES Test Results with Dispersion I Grns. Compound to Insolubilize Compound Insolubili- Chemical zation Test A Solubilization Test B Dispersion II Containing 25 mg. Silver Halide Photosolubilization Test n-Propyl mercaptam i-Propyl mercaptan. n-Butyl mercaptan. i-Butyl mercaptaru- Sec. butyl mercaptan t-Butyl mercaptan n-Amyl mercaptan 2-Pentanethiolsee. amyl mercaptan t-Amyl mercaptan n-Hexyl mereaptan n-Heptyl mercoptan. n-Octyl mercaptan... t-Octyl mereaptan. Z-ethyl-l-hexanethiol.

n-Nonyl mereaptan n-D ecyl mercaptan.

n-Undecyl mercaptan n-Dodecyl mercaptan.

t-Dodeeyl mercaptarn- Benzyl mercaptan oMethyl hcnzyl mereaptan p-Methyl benzyl mercaptan.

o-Ethyl benzyl mercaptan p-Ethyl benzyl mercaptan p-Methoxybenzyl mercupt'm Ethyl mercapto acetate Methyl mercapto acetate ISo-oc'tyl thioglyeolate.-

. Iso-octyl-S-mercaptopropionate Mercapto-his-[ethyl mercapto acetate] sulfide 32. Di-t-nonylpolysulfide 33. Thiobenzoic acid 34. 2,1nercapt0 suecinie acid 35. l-thioglyeerol 36. (Ethyl mercapto)-acetie acid Preparation described in Hatchard, U.S. appln. Ser. No. 146,370, Oct. 19, 1961.

EXAMPLE IV An emulsion as described in Dispersion II, Example HI, Was redispersed in a gelatin solution which contained 47 g. gelatin per mole of the silver halide. A pH 6.01:1 was maintained While dispersing min. at 110 F. The emulsion was brought to 2320 g. by addition of Water and the temperature adjusted to 120 F. Fourtenths of a gram of n-dodecyl mercaptan was added per mole of silver halide from a 1% by weight ethanol solution. Chrome alum hardener was added and the emulsion was diluted with Water to a total weight of 2334 g. per mole of silver halide. This emulsion Was applied at a coating weight of 4-6 mg. of silver per square decimeter on 0.004 inch thick polyester photographic film base as described in Example I. The coating, after imagewise exposure, showed a greater rate of fixing in a 1.0 N (0.5 M) aqueous solution of sodium thiosulfate in exposed areas than in the unexposed areas so as to form a positive silver halide image. Subsequent flashing to White light, followed by treatment with a reducing agent (a conventional photographic developing solution containing 1- phenyl-4-methyl-3-pyrazolidone and hydroquinone), resulted in the formation of a positive image of metallic silver. The optical densities of completely unexposed areas and heavily exposed areas of the film, as determined using a Western Electric RA-lOO-C Densitometer, Were 0.21 and 0.10, respectively.

The silver halide photosoluble elements of this invention differ from conventional silver halide emulsions containing anti-fogging agents in that the insolubilizing compounds used in the photosoluble elements are present in substantially greater than fog-inhibiting amounts, the latter amounts being the maximum quantity which provides low fog Without serious loss in speed and photographic quality. For this reason it is not practical to use photosoluble elements in place or" ordinary silver halide photographic materials. When photosoluble elements are exposed and processed normally, development proceeds slowly and incompletely to give a negative silver image having much less speed and lower density. In addition,

fixing is slower and may be incomplete for practical fixing times. Thus, photosoluble elements require longer conventional processing times and give slower speed, inferior quality images when compared to ordinary silver halide photographic elements.

The novel photographic compositions of this invention have numerous advantages. A primary advantage is the simplicity of their preparation. They can be exposed and processed to images under ordinary room light conditions.

The photographic processes applicable to the compositions and elements of the invention likewise have advantages over previously known systems based on selective reductions of exposed silver halide for forming either direct positive or negative images without resorting to the special effects and sensitizing procedures previously used for preparing such images. In addition, since image formation does not require selective reduction, this present process is not limited to the use of certain photographic developing agents but may be accomplished by using a Wide range of reducing agents. Many such compounds are of very low cost and can be used to form images of much higher covering power than customary, thus effect ing important economies in processing, as well as greatly increasing the efiiciency of the silver image With a resultant increase in sensitivity.

Another advantage of the compositions and elements of this invention is that they may be processed to form silver halide or silver images without the requirement of special equipment but instead conventional equipment and apparatus can be used. A further advantage is that the processes can be carried out successfully by photographic technicians and photographers of ordinary skill. A still further advantage is that the processes utilize conventional reducing agents, e.g., developers and fixing agents. Still additional advantages will be apparent from the above description of the invention.

This application is a continuation-in-part of my copending application Ser. No. 158,132, filed December 8, 1961, for Photographic Compositions and Processes, now abandoned.

I claim:

1. A photographic silver halide composition before exposure to actinic radiation containing in greater than fog-inhibiting amounts an organic mercaptan containing 1-2 mercapto groups, having a molecular Weight greater than 75 and being taken from the group consisting of alkyl mercaptans and organic mercaptans containing two tercaptan groups linked to carbon, the silver mercaptide of said organic mercaptaue being of lower solubility in water than silver chloride; said organic mercaptan being present in such an amount, in terms of the ratio of its Weight to the surface area of the silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide dispersion, 70/30 mole percent, gelatin dispersion containing 0.29 mg. of Ag in /2 ml., and said silver chlorobromide dispersion is treated with 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag and 100 mg. of sodium thiosulfate, at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively trea.ed with 5% by weight aqueous sodium hypochlorite and by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag, mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate, after vigorous agitation of both dispersions for seconds at 25 C.; said composition being free from a silver halide developing agent.

2. A photographic element beariiu a layer before exposure to actinic radiation comprising silver halide containing in greater than fog-inhibiting amounts an organic rnercaptan containing 1-2 mercapto groups, having a molecular weight greater than 75 and being taken from the group consisting of alkyl mercaptans and organic mercaptans containing two mercaptan groups linked to carbon, the silver salt of said organic mercaptan being of lower solubility in water than silver chloride; said organic mercaptan being present in such an amount, in terms of the ratio of its weight to the surface area of the silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide dispersion, 70/30 mole percent, gelatin dispersion containing 0.29 mg. of Ag in Vz ml., and said silver chlorobromide dispersion is treated with 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag and 100 mg. of sodium thiosulfate, at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5% by weight aqueous sodium hypochlorite and 10% by weight aqcuous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag, 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate, after vigorous agitation of both dispersions for 30 seconds at 25 C.; said composition being free from a silver halide developing agent.

3. An element according to claim 2 wherein said silver halide is silver chlorobromide.

4. An element according to claim 2 wherein said organic mercaptan is an alkyl mercaptan of 3-12 carbon atoms.

5. An element according to claim 2 wherein said or- 2 ganic compound is an organic mercaptan containing two mercaptan groups linked to carbon.

6. An element according to claim 2 wherein the layer is a gelatino-silver chlorobromide emulsion layer.

7. An element according to claim 2 wherein the layer is a gelatino-silver chlorobromide emulsion layer having a gelatin-silver halide ratio from 3:1 to 1:30 by weight.

8. A photographic silver halide emulsion before exposure to actinic radiation comprising silver halide cry-1; tals previously made less soluble in a silver halide solvent by treatment with 0.125 gram to 314 grams and substantially greater than fog-inhibiting amounts, per mole of silver halide, of an organic mercaptan containing l-2 mercapto groups, having a molecular weight greater than and being taken from the group consisting of alkyl mercaptans and organic mercaptans containing two mercaptan groups linked to carbon, the silver salt of said organic mercaptan being of lower solubility in water than silver chloride; said organic mercaptan being present in such an amount, in terms of the ratio of its weight to the surface area of the silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide dispersion, 70/30 mole percent, gelatin dispersion containing 0.29 mg. of Ag in /2 ml., and said silver chlorobromide dispersion is treated with 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag and 100 mg. of sodium thiosulfatc, at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5% by weight aqueous sodium hypochlorite and 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag, 25 mg. of sodium hypochlorite and 100 mg. oi sodium thiosulfate, after vigorous agitation of both dispersions for 30 seconds at 25 C.; said composition being free from a silver halide developing agent.

9. An emulsion according to claim 8 wherein the solubility of the silver halide crystals is affected by exposure to actinic radiation to such an extent that at least 20% of the less soluble crystals remain when of the more soluble crystals have dissolved in 10% aqueous sodium thiosulfate.

References tilted in the file of this patent UNITED STATES PATENTS 2,214,446 Albers et a1. Sept. 10, 1940 3,008,829 Clementi et al Nov. 14, 1961 3,046,130 Dersch et al July 24, 1962 3,063,837 Lassig et al. Nov. 13, 1962 3,080,230 Haydn et al Mar. 5, 1963 OTHER REFERENCES Land: A New One-Step Photographic Process, Journal of the Optical Society of America, vol. 37, No. 2, pages 61-77, February 1947.

Keelan: The Journal of Photographic Science, vol. 5, November 1, December 1957, pages 144 and 145.

Faerman et al.: Chem. Abst., vol. 52, No. 2, Col. 937d; January 25, 1958 (abstract of Otdel Chim. Nauk 5, 107- 13 (L957)). 

1. A PHOTOGRAPHIC SILVER HALIDE COMPOSITION BEFORE EXPOSURE TO ACTINIC RADIATION CONTAINING IN GREATER THAN FOG-INHIBITING AMOUNTS AN ORGANIC MERCAPTAN CONTAINING 1-2 MERCAPTO GROUPS, HAVING A MOLECULAR WEIGHT GREATER THAN 75 AND BEING TAKEN FRM THE GROUP CONSISTING OF ALKYL MERCAPTANS AND ORGANIC MERCAPTANS CONTAINING TWO MERCAPTAN GROUPS LINKED TO CARBON, THE SILVER MERCAPTIDE OF SAID ORGANIC MERCAPTANE BEING OF LOWER SOLUBILITY IN WATER THAN SILVER CHLORIDE; SAID ORGANIC MERCAPTAN BEING PRESENT IN SUCH AN AMOUNT, IN TERMS OF THE RATIO OF ITS WEIGHT TO THE SURFACE AREA OF THE SILVER HALIDE CRYSTALS, THAT WHEN ADMIXED IN SUCH RATIO WITH AN AQUEOUS SILVER CHLOROBROMIDE DISPERSION, 70/30 MOLE PERCENT, GELATIN DISPEERSION CONTAINING 0.29 MG. OF AG IN 1/2 ML., AND SAID SILVER CHLOROBROMIDE DISPERSION IS TREATED WITH 10% BY WEIGHT AQUEOUS SODIUM THIOSULFATE, SO THAT THE RESULTING MIXTURE CONTAINS 0.29 MG. OF AG AND 100 MG. OF SODIUM THIOSULFATE, AT LEAST THREE TIMES THE AMOUNT OF SILVER CHLOROBROMIDE REMAINS UNDISSOLVED AS COMPARED WITH A SIMILAR DISPERSION SUCCESSIVELY TREATED WITH 5% BY WEIGHT AQUEOUS SODIUM HYPOCHLORITE AND 10% BY WEIGHT AQUEOUS SODIUM THIOSULFATE, SO THAT THE RESULTING MIXTURE CONTAINS 0.29 MG. OF AG. 25 MG. OF SODIUM HYPOCHLORITE AND 100 MG. OF SODIUM THIOSULFATE, AFTER VIGROUS AGITATION OF BOTH DISPERSIONS FOR 30 SECONDS AT 25*C.; SAID COMPOSITION BEING FREE FROM A SILVER HALIDE DEVELOPING AGENT.
 2. A PHOTOGRAPHIC ELEMENT BEARING A LAYER BEFORE EXPOSURE TO ACTINIC RADIATION COMPRISING SILVER HALIDE CONTAINING IN GREATER THAN FOG-INHIBITING AMOUNTS AN ORGANIC MERCAPTTAN CONTAINING 1-2 MERCAPTO GROUPS, HAVING A MOLECULAR WEIGHT GREATER THAN 75 AND BEING TAKEN FROM THE GROUP CONSISTING OF ALKYL MERCAPTANS AND ORGANIC MERCAPTANS CONTAINING TWO MERCAPTAN GOUPS LINKED TO CARBON, THE SILVER SALT OF SAID ORGANIC MERCAPTAN BEING OF LOWER SOLUBILITY IN WATER THAN SILVER CHLORIDE; SAID ORGANIC MERCAPTAN BEING PRESENT IN SUCH AN AMOUNT, IN TERMS OF THE RATIO OF ITS WEIGHT TO THE SURFACE AREA OF THE SILVER HALIDE CRYSTALS, THAT WHEN ADMIXED IN SUCH RATIO WITH AN AQUEOUS SILVER CHLOROBROMIDE DISPERSION, 70/30 MOLE PERCENT, GELATIN DISPERSION CONTAINING 0.29 MG. OF AG IN 1/2 ML., AND SAID SILVER CHLOROBROMIDE DISPERSION IS TREATED WITH 10% BY WEIGHT AQUEOUS SODIUM THIOSULFATE, SO THAT THE RESULTING MIXTURE CONTAINS 0.29 MG. OF AG AND 100 MG. OF SODIUM THIOSULFATE, AT LEAST THREE TIMES THE AMOUNT OF SILVER CHLOROBROMIDE REMAINS UNDISSOLVED AS COMPARED WITH A SIMILAR DISPERSION SUCCESSSIVELY TREATED WITH 5% BY WEIGHT AQUEOUS SODIUM HYPOCHLORITE AND 10% BY WEIGHT AQUEOUS SODIUM THIOSULFATE, SO THAT THE RESULTING MIXTURE CONTAINS 0.09 MG. OF AG. 25 MG. OF SODIUM HYPOCHLORITE AND 100 MG. OF S ODIUM THIOSULFATE, AFTER VIGOROUS AGITATION OF BOTH DISPERSIONS FOR 30 SECONDS AT 25*C.; SAID COMPOSITION BEING FREE FROM A SILVER HALIDE DEVELOPING AGENT. 